What should have been a simple Windows 8.1 upgrade ended up being a few hours of fiddling w/ Windows to get rid of a boot crash in the igdkmd64.sys (Intel Graphics Kernel Mode Driver). Uninstalling the Intel HD video driver in Device Manager by booting into Safe Mode got rid of this crash but Windows then booted up into a blank screen that you couldn't do anything with.

But to get into Safe Mode, you have to boot off a Windows 8 install disk, or to get the old F8 key on boot functionality back, you have to boot into a Windows 8 install disk and execute: bcdedit /set {default} bootmenupolicy legacyBut in Safe Mode, you can no longer uninstall programs unless you install SafeMSI.

It's best that you do these two steps before you install the Windows 8.1 update. It's also a good idea to grab the latest Windows 8.1 drivers for your motherboard so you can install them after you install Windows 8.1. Uninstall LucidLogix Virtu and the Intel HD drivers before you do the update and you should be able to avoid this pain :-P

And after the update, the Windows and Program Files directories become uncompressed. If you still want to compress them to save space, boot off a rescue CD/USB boot setup and recompress everything with "compact /s /c /a /i *"

If you're using VirtualBox with a bridged adapter, you'll also have to uninstall/reinstall it or it won't be able to find your system's network adapter to bridge to. Doing a repair on the installation does not work.